Multicast is a method for sending data from a source to many destinations. With multicast, the same data can be sent to many subscribers by sending only once, thus network resources can be saved. According to the 3GPP (3rd Generation Partnership Project) standard, a node in a wireless access network can be connected to a plurality of central network nodes with Iu-Flex technology. For example, a General Packet Radio Services (GPRS) Radio Network Controller (RNC) or Universal Mobile Telecommunication System (UMTS) Base Station Controller (BSC) can be connected to a plurality of Serving GPRS Support Nodes (SGSN). In this way, when MBMS (Multimedia Broadcast/Multicast Service) is implemented in an Iu-Flex-based network environment, MBMS traffic may be sent from a plurality of SGSNs to the same RNC, which results in a waste of network bandwidth resources. In order to solve this problem, many methods have been proposed for implementing MBMS in Iu-Flex-based network environments.
The first method utilizes a default SGSN, i.e., during the process of activating or relocating/switching multicast traffic, the RNC determines whether to establish multicast traffic or to insert the multicast traffic into an existing multicast traffic. To ensure that the RNC receives multicast data from only one SGSN, the RNC appoints a “Default SGSN”, which is used to establish a multicast traffic channel in advance. At the same time, the RNC establishes an RAB link to the SGSNs where the subscribers are registered to maintain the signal connections. However, the method may result in difficulty in traffic-based accounting, because the SGSNs where the subscribers are registered don't “know” the data volume transmitted through the “default SGSN”.
The second method is to bypass the SGSNs. In this method, SGSNs participate in the alternation of multicast signals, but the GGSNs send multicast data directly to the RNC without the participation of the SGSNs. Because the RNC can connect with the GGSNs, the internal structure of the network will be disclosed when subscribers roam between the GGSNs and the SGSNs, which will result in network security problems. At the same time, the method may also result in difficulty in traffic-based accounting because the SGSNs where the subscribers are registered don't “know” the data volume transmitted through the “default SGSN”.
The third method is to let the RNC choose one from multicast traffics. In this method, the RNC keeps receiving a data stream from SGSNs, but chooses one of them and forwards it to multicast subscribers. A disadvantage of this method is network resources cannot be utilized effectively.
The fourth method is to let the RNC use a single connection to one of the SGSNs. In this method, when the MBMS data transmission begins and the RNC detects sending requests from many SGSNs, the RNC will establish connections to individual SGSNs but only establish a multicast RAB to one of the SGSNs, and no TAB is established between RNC and other SGSNs, but other SGSNs can receive multicast data from GGSNs and create traffic-based accounting information for specific subscribers. In an Iu-Flex-based network environment, even though a plurality of subscribers in the same multicast subscriber group are connected to the same RNC, they may be served by a plurality of SGSNs simultaneously. In this case, the MBMS message parameters at the SGSNs should be identical. However, synchronization among SGSNs and parameter consistency for the MBMS will increase the complexity of control and degrade the processing efficiency.